Flow and edge control in vertical sheet drawing

ABSTRACT

Four pairs of electrodes are provided, protruding through side walls of a drawing kiln. One pair on each side is positioned to the front of the meniscus, and the other pair is to the rear. Electric current is supplied to each of the above-mentioned pairs, whereby electrical heating is provided to spring or edge zones of the glass in the drawing kiln. The manner of heating described prevents devitrification, provides warmer edges, and makes it possible to adjust as desired the electric heating effect in a given spring or edge zone.

United States Patent 3,692,510 FLOW AND EDGE CONTROL IN VERTICAL SHEET DRAWING Arnold J. Goldberg, Lower Burrel], and Leonard A. Knavish, Pittsburgh, Pa., assignors to PPG Industries, Inc., Pittsburgh, Pa.

Filed Sept. 1, 1970, Ser. No. 68,713 Int. Cl. C03b 15/08 US. Cl. 65203 1 Claim ABSTRACT OF THE DISCLOSURE Four pairs of electrodes are provided, protruding through side walls of a drawing kiln. One pair on each side is positioned to the front of the meniscus, and the other pair is to the rear. Electric current is supplied to each of the above-mentioned pairs, whereby electrical heating is provided to spring or edge zones of the glass in the drawing kiln. The manner of heating described prevents devitrification, provides warmer edges, and makes it possible to adjust as desired the electric heating effect in a given spring or edge zone.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to apparatus for making sheet glass by a continuous process wherein the sheet is drawn vertically from a molten bath.

(2) Description of the prior art From Koupal et al. US. Patent No. 2,114,715, it is known to provide a drawing kiln with two pairs of elec trodes, each pair protruding through one of the side walls of the kiln in the vicinity of the meniscus, with one of the electrodes of a pair being to the front of the meniscus and the other behind it. While such an arrangement may be used to obtain a heating effect to warm the edges and prevent devitrification, such apparatus does not make it possible to obtain the effects observed with the present invention.

SUMMARY OF THE INVENTION DESCRIPTION OF THE DRAWING A complete understanding of the invention may be obtained from the foregoing and following description thereof, taken together with the appended drawing in which:

FIG. 1 is an elevational view, partly schematic, of a drawing kiln provided with heating electrodes in accordance with the present invention, and

FIG. 2 is a plan view, partly schematic, showing apparatus in accordance with FIG. 1 and its connection to an electrical source.

3,692,510 Patented Sept. 19, 1972 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a drawing kiln 2 having therein a bath 4 of molten glass in which there is totally submerged a draw bar 6 and from which glass is drawn in a meniscus region 8, passing between L blocks 10 and forming a sheet 12. A shutoff is indicated at 14. The parts described above may be considered conventional.

Shown in FIG. 1 is a first pair 16, 18 of heating electrodes that are positioned to the front of meniscus region 8. Also shown are a pair 20, 22 of heating electrodes positioned to the rear of the meniscus region 8.

As seen in FIG. 2, the kiln 2 is also provided with a corresponding third pair of electrodes 24, 26 to the front of the meniscus region and a fourth pair 28, 30 to the rear of the meniscus region 8. As may also be seen from FIG. 2 electric power is provided to the above-mentioned pairs of electrodes from a source 34 of electrical power in such manner that electric current passes between the ones of the electrodes defined above as comprising said pairs. By suitable means, such as the operation of the variable resistances 36, the amount of electrical power supplied to a given one of the four pairs of electrodes mentioned above may be suitably adjusted, as may be desirable or necessary in a given case.

The equipment described above may be operated, as those skilled in the art will appreciate, to increase or decrease the temperature of the glass flowing toward the meniscus region 8 in a desired one or ones of the four regions of flow associated with the four pairs of electrodes. It is possible, for example, by increasing the flow of power to the electrodes 28, 30, to warm the back-side flow of glass approaching the meniscus region 8 near one edge of the sheet 12, and if desired at the same time, by suitably adjusting a different one or different ones of the various resistors 36, to permit the front-side flow near the opposite side wall to become cooler. Such an effect could not be obtained with the above-mentioned equipment of the prior art.

The electrodes 16 through 30 mentioned above may be made of suitable material, such as platinum, and may project into the furnace from the side wall of the kiln by a suitable distance, such as about 4 inches.

The elctrodes may be spaced as desired to obtain desired effects, but satisfactory results may be obtained if electrodes 16, 24 are positioned 12 inches below the surface of the bath and 12 inches from the front wall 38 of the kiln 2. The electrodes 20 and 30 may be positioned at the same depth within the glass, spaced 45 inches from the plane of the sheet 12. The electrodes 18 and 26 may be positioned 6 inches below the surface 40 of the bath 4, and 15 inches toward the front wall 38 from the plane of the sheet 12. The electrodes 22 and 28 may be positioned 6 inches below the surface 40 and 15 inches to the rear side of the plane of the sheet 12. The foregoing specific example is on the basis of a bath 58 inches deep and inches wide. Satisfactory results may be obtained with the use of a source 34 of twenty-kilowatt capacity, it not being necessary to use in most instances more than a fraction of the power available from such source.

We claim as our invention:

1. Apparatus for controlling the temperature of frontside and rear-side edge flows of glass in a kiln in a verticaldrawing process for the manufacture of a sheet of sheet glass, said apparatus comprising, in combination,

a first pair of electrodes projecting through a first side Wall of said kiln and located in the front-side edge How of glass to a first edge of said sheet,

a second pair of electrodes projecting through said first side Wall of said kiln and located in the back-side edge flow of glass to said first edge of said sheet,

a third pair of electrodes projecting through a second and opposite side wall of said kiln and located in the front-side edge flow of glass to a second and opposite edge of said sheet,

a fourth pair of electrodes projecting through said second side wall of said kiln and located in the back-side edge flow of glass to said second edge of said sheet,

4 a source of electrical power connected to each of said pairs of electrodes so that electrical current from said source flows between the electrodes of each said pair and through the glass flowing therebetween, and means for separately varying the amount of electrical power supplied to each of said pairs of electrodes.

References Cited UNITED STATES PATENTS 1,781,917 11/1930 Drake 65203 X 2,111,860 3/1938 Kilian 65203 X ARTHUR D. KELLOGG, Primary Examiner 

